For producing brushes, in particular toothbrushes, but also brushes for use in the household, two methods are prevailing in the field, that is the fastening of the bristle tufts by using an anchor (small metal plates or wire loop) or without using an anchor. As opposed to using an anchor, in the anchor-free method the bristle tuft is not folded and fastened in the bristle carrier on the folding location thereof, but is fixed with an end thereof at the bristle carrier by gluing or thermal processing. According to a common method prevailing in the field, the bristle carrier has openings through which the bristle tufts are inserted. The bristle tufts then protrude with the back side thereof from the openings and are heated on the back side of the bristle carrier. The thermoplastic material of the bristles is thus melting, whereby the bristles fuses materially with each other, and this results in a thickening, thus it is not possible to pull-off single bristles towards the front side. In general, said plurality of bristle tufts are liquified on the back side by using hot air or a hot punch, so that the material of the respective bristle tufts merges into each other and creates a kind of layer made of the liquified bristle ends on the back side thereof. This back side is then covered, in particular overmoulded.
The disadvantage of this solution is that due to the required covering of the back side a considerable additional effort is required regarding the method and the apparatus. However, it is to be noted that especially for toothbrushes the transition surfaces between adjacent layers have to be formed without gaps as far as possible to eliminate hygienic problems.
The term “bristle carrier” is to denote the part of the final brush, which carries the bristle or the bristle tufts. The bristle carrier may thus form the complete brush body, for a toothbrush this is the integrally injection moulded part made of handle, neck and head, or also only a pre-manufactured part of the later brush body. In the latter case, the bristle carrier is generally a thin plate made of thermoplastic resin, which is provided with one or more openings for stuffing it with one or more bristles or bristle tufts. After stuffing and fastening of the bristles, the plate-like bristle carrier is then either inserted in the pre-manufactured bristle body, which for example includes a respective recess for the plate-like bristle carrier. Alternatively to this, and this is the usual case, the plate-like bristle carrier is overmoulded and thus results in a bristle body composed of the prefabricated bristle carrier and an injection moulded rest.
CH 672 579 A5 proposes a method for fastening bristle tufts in the bristle carrier by means of a small anchor plate. This means, the bristle tuft is folded, and the small anchor plate, which presses itself in the wall of the anchoring opening, is arranged in the folding area, and thus the bristle tuft is finally fixed on the bristle carrier. However, in order to close the opening on the front face and the front side of the bristle carrier in a more refined way, so that no bacteria or spores may find a hold and may proliferate, a bead around the bristle carrier, which surrounds the anchoring opening and protrudes from the front face, is to be pressed inwards. However, the bristle tuft itself is not fastened by this reshaping of the bead, but by the anchor itself. The single bristle tufts are subsequently punched into the bristle carrier by using a stuffing tool, which pushes the folded bristle tufts through a pipe. The pipe itself may then have a heating device on the front face thereof, which is only abutting on the bead and causes it to melt or plasticize, and subsequently presses the bead radially inwards.
In addition to the possibilities of an anchorless fastening of the bristle or the bristle tuft on the bristle carrier mentioned above, as second method has been developed in theory, which however has never been realized, that is striking the bristle tufts into the bristle carrier, which includes openings and which is preheated. After striking the bristle tufts into the soft bristle carrier, the bristle carrier is exposed to pressure by means of a press on the front side of the bristle carrier, from which front side the bristle tufts are protruding, so that the soft material around the rim of openings is compressed and the cross-sections of the openings are reduced. Referring to this, some concepts will be presented in the following.
In DE 198 53 030 A1 the bristle tufts comprise bristles, which are fused together to form a thickening, on the back side thereof. The bristle carriers include openings, in which cylinder-shaped protrusions of a heating are introduced before striking the bristle tufts without contacting the rim of the opening. By this radiation heat the inward rim of the openings is locally heated. The bristle carrier is heated in the region of the rim to a structure-changing temperature, for example the softening temperature. By means of this temperature increase, the hole is to be reduced in its cross-section, thus the bristle tuft has to penetrate into the wall during striking. After removing the heating device, the bristle tufts are then striked into the openings by using the thickened ends thereof, wherein the cross-section of the thickening is larger than the cross-section of the opening, so that the thickening penetrates into the soft portion of the rim, which defines the opening and encompasses it, that is in the respective wall. Then the front surface of the bristle carrier is reshaped by using the punch, thus the material of the bristle carrier is pressed against the bristle tufts and anchors them.
From U.S. Pat. No. 5,224,763 a similar method is known, where a bristle carrier includes a bead-like protruding rim of the opening. Here also the rim of the opening is heated by means of a pin-shaped heating element protruding into the opening or by using hot air. The cross-section of the opening itself is smaller than the thickened end of the bristle tufts, thus it is fixed after striking into the wall of the soft opening. Then the support for the bristle tufts compresses the heated circumferential bead, so that additional material is available to close the opening on the transition to the front face of the bristle carrier.
From EP 0 355 412 A1 a method is known, where the thickened end of the bristle tuft and/or the rim of the opening in the bristle carrier are heated, wherein the dimensions and temperatures are selected in a way, that after striking the thickened end, the rim of the opening presses inwards and thus encompasses the thickened end similar to a snap fit and receives the thickened end in a form-fitting way.
EP 0 472 557 B1 proposes to penetrate in a plate-shaped bristle carrier made of resin by using a heated punch, which includes pins, thus the pins form openings for receiving the bristle tufts. The bristle tufts are then pushed into the punched openings, which are still hot, and the melting is raised around the thickening of the bristle tufts. Furthermore, a die plate may be pressed against the upper side of the bristle carrier, in order to also shape the melting. Here it is especially preferred, that on the upper side of the not yet reshaped bristle carrier protrusions or beads are projecting, which form material, that is available as material, which is pressed towards the opening.
In the method according to DE 34 22 623 A1 a bristle carrier, which is plate-shaped and is configured without openings, is fused with bristle tufts consisting of the same plastic material as the bristle carrier. A heating tool is moved between the sides of the bristle carrier and of the bristle tufts, which have not yet been fused together, thus both are fused. Then, the bristle tufts are pressed into the molten material of the bristle carrier.